1. Field of the Invention
The present invention relates to a recording apparatus for recording a video signal, an audio signal and the like onto an optical recording disk, and relates, more particularly to, a technique for reducing an influence of a tilt of a disk in a circumferential direction applied to a recording and reproduction of information, in a recording apparatus for carrying out a recording and reproduction of information by transmitting a laser beam onto a transparent substrate of the disk.
2. Description of the Related Art
A recording and reproduction of information onto and from an optical disk is carried out by irradiating laser beams onto the optical disk. The laser beams irradiated onto the optical disk are collected on the optical disk.
In order to increase the recording density of information recorded on the optical disk, the numerical aperture of an objective lens is made larger and the diameter of a light spot formed on the optical disk is made smaller. With this arrangement, it is possible to record the information on the optical disk as a smaller mark. As a result, it is possible to increase a spatial frequency in the circumferential direction of a recording signal and to narrow a track pitch. This method has been widely known in general as a method of increasing the recording density of information.
However, the increasing the numerical aperture of an objective lens has a problem of making larger an influence of a tilt of the disk applied to a recording and reproduction of information. More specifically, when a tilt is generated on the disk, the quantity of aberration generated at a light spot becomes large, and when the diameter of the light spot becomes larger, the distribution of the light spot does not become symmetrical. As a result, it becomes difficult to accurately carry out a recording and reproducing processing of information.
Regarding a tilt of a disk in a radial direction of the disk, it is possible to correct the tilt by adjusting the angle of a pickup or the disk whenever necessary, so that it is possible to reduce an influence of this tilt. On the other hand, regarding a tilt of the disk in a circumferential direction of the disk, it is difficult to correct this tilt by a mechanical adjustment as the speed of variation of the tilt is fast.
When information is recorded on an optical disk in the status where the disk is tilted in a circumferential direction, there is a case where a mark to be recorded on the disk by an irradiation of laser beams is deviated from a position at which the mark should be originally recorded. Such a deviation in the recording spot appears as a jitter of information at the time of reproducing the information, and this jitter degrades the quality of a reproduced signal. A problem like this also occurs when an optical disk has not a flat surface but has a variation in the thickness of the disk, not only when the disk is tilted.
Further, the quantity of aberration generated by the tilt of the optical disk is proportional to the thickness of a transparent substrate constituting the optical disk. Therefore, it is possible to make smaller the quantity of the aberration by reducing the thickness of the transparent substrate. However, when the thickness of the transparent substrate is made smaller, there arises a problem that the performance of the optical disk is lowered due to a hurt or a stain on the disk surface.
Further, the quantity of aberration may be made smaller by reducing the total thickness of the optical disk. However, when the total thickness of the disk is reduced, there arises a problem that the disk as a whole or the disk substrate is easily distorted.
It is an object of the present invention to provide an optical recording apparatus capable of correctly recording information onto a recording disk even when there is generated a tilt in the recording disk in a circumferential direction of the disk.
An optical recording apparatus in accordance with the present invention includes: a tilt detecting device for detecting a circumferential direction component of a tilt of a recording medium with respect to a laser beam light axis; a recording pulse signal generating device for generating a recording pulse signal by coding an information signal to be recorded and outputting the generated recording pulse; a modulating device for receiving the recording pulse from the recording pulse signal generating device, and modulating an intensity of a laser beam based on the received recording pulse signal; a laser beam irradiating device for applying the modulated laser beam onto the recording medium; and a recording pulse signal control device for controlling a sending timing at which the recording pulse signal is sent from the recording pulse signal generating device to the modulating device, based on the circumferential direction component detected by the tilt detecting device.
In this optical recording apparatus, the recording pulse signal generating device carries out an encoding of an information signal to be recorded, and generates a recording pulse signal. The modulating device modulates the intensity of a laser beam based on this recording pulse signal. The laser beam irradiating device irradiates the laser beam whose intensity has been modulated, to the recording medium. As a result, the information signal is recorded.
The recording of an information signal onto a recording medium is carried out by first heating the recording medium by a laser beam to change optical characteristics of the material of the recording medium, thereby to form marks onto the recording medium. Thus, the information signal is recorded onto the recording medium. Accordingly, when the irradiated surface of the recording medium has a tilt in the circumferential direction of the disk, the center of the spot light quantity of the laser beam is deviated from a proper position due to a generation of aberration.
In the above aspect of the optical recording apparatus according to the present invention, the deviation of the center of the light quantity of the light spot is overcome in the following manner. When the tilt detecting device has detected a circumferential direction component of a tilt of the optical disk with respect to the laser beam light axis, the recording pulse signal control device controls the sending timing of the recording pulse signal to the modulating device, based on a detection output of the circumferential direction component of the tilt. For example, when the center of the light quantity of the light spot has deviated in a direction to gain time, the recording pulse signal control device delays the sending timing of the recording pulse signal from the reference timing. On the other hand, when the center of the light quantity has deviated in a direction to lose time, the recording pulse signal control device advances the sending timing of the recording pulse signal from the reference timing.
As a result, a temperature gradient on the recording medium changes in a similar manner to that of the case where there is no tilt, so that an edge position of a mark to be recorded becomes at a proper position. Accordingly, it is possible to prevent an occurrence of a jitter at the time of a reproduction and to prevent an increase in the error rate. Further, it is possible to carry out a stable recording and reproduction of an information signal even when a disk having a large deformation quantity is used. Furthermore, it is possible to compensate the disk for a warp, so that it is possible to carry out a recording and reproduction of an information signal onto and from a thin disk.
The aforementioned optical recording apparatus in accordance with the present invention, the circumferential direction component may include a component indicating a tilt angle of a recording surface of the recording medium. Furthermore, when the recording surface at a front side of a laser beam in a relatively proceeding direction of the laser beam is tilted in a direction to leave away from the laser beam irradiating device from a reference horizontal position with the light axis as a center, the recording pulse signal control device may delay the sending timing from a predetermined reference timing as the tilt angle becomes larger. Moreover, when the recording surface at the front side of a laser beam in a relatively proceeding direction of the laser beam is tilted in a direction to come closer to the laser beam irradiating device from a reference horizontal position with the light axis as a center, the recording pulse signal control device may advance the sending timing from a predetermined reference timing as the tilt angle becomes larger.
When the recording surface of a recording medium at the front side of a laser beam in a relatively proceeding direction of the laser beam is tilted in a direction to leave away from the laser beam irradiating device from the reference horizontal position with the light axis as a center, the center of the spot light quantity of the laser beam is positioned at a rear side of the laser beam in a relatively proceeding direction thereof with respect to the recording medium from the center of the light axis, due to the influence of aberration. In this case, the recording pulse signal control device delays the sending timing of the recording pulse signal from a predetermined reference timing as the tilt angle in this direction becomes larger. As a result, the mark is recorded at a proper position. On the other hand, when the recording surface at the front side of a laser beam in a relatively proceeding direction of the laser beam is tilted in a direction to come closer to the laser beam irradiating device from the reference horizontal position with the light axis as a center, the center of the spot light quantity of the laser beam is positioned at a front side of the laser beam in a relatively proceeding direction of the laser beam with respect to the recording medium from the center of the light axis, due to the influence of aberration. In this case, the recording pulse signal control device advances the sending timing of the recording pulse signal from a predetermined reference timing as the tilt angle in this direction becomes larger. As a result, the mark is recorded at a proper position. Thus, it is possible to record the mark at a proper position by canceling a deviation of the center of the spot light quantity of the laser beam due to the aberration.
In the aforementioned the optical recording apparatus in accordance with the present invention, the recording pulse signal control device may include (i) a memory device having a plurality of memory units, and (ii) a data read/write control device for sampling the recording pulse signal generated by the recording pulse signal generating device at a predetermined sampling rate and then writing the sampled recording pulse signal into any of the plurality of memory units in the memory device, and for reading the sampled recording pulse signal from any of the plurality of memory units in the memory device at a predetermined reading rate. Furthermore, the data read/write control device may repeat a writing of the sampled recording pulse signal into any of the plurality of memory units and reading of the sampled recording pulse signal from any of the plurality of memory units, and changes a predetermined time interval provided between an end of the writing and a start of the reading to change the sending timing.
The recording pulse signal generated by the recording pulse generating device is sampled at a predetermined sampling rate by the data read/write control device, and is written into the memory device at each predetermined memory unit. Further, the sampled data of the written recording pulse signal is read for each predetermined memory unit in the memory device at a predetermined reading rate by the data read/write control device.
Then, the data read/write control device provides a predetermined time interval between an end of the writing and a start of the reading in each memory unit, and reads out the data by reducing this time interval from a predetermined reference time interval, thereby to advance the sending timing of the recording pulse signal. The data read/write control device also reads out the data by extending the time interval from the predetermined reference time interval, thereby to delay the sending timing of the recording pulse signal. Thus, the data read/write control device adjusts the sending timing by changing the read timing after the recording pulse signal has been once stored in the memory device. As a result, it is possible to easily carry out the control of the sending timing.
In the aforementioned the optical recording apparatus in accordance with the present invention, the recording pulse signal control device may further includes (i) a conversion table for showing a relationship between a tilt angle and a quantity for changing a sending timing, and (b) a conversion device for converting a value of the tilt angle detected by the tilt detecting device into a quantity of change of the predetermined time interval, based on the conversion table.
When a detection output for showing the degree of a tilt angle has been obtained by the tilt detecting device, the recording pulse signal control device converts the degree of the tilt angle into a changing quantity of the time interval, based on the conversion table. As mentioned above, because the relationship between the value of a detection output of the tilt detecting device and the changing quantity of the time interval has been determined in advance by the conversion table as described above, it is possible to promptly obtain the changing quantity of the time interval, so that it is possible to carry out a prompt control of the sending timing.
The nature, utility, and further feature of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.